Halichondrins have been disclosed as having anti-cancer and antimitotic activity (Chem. Rev. 2009, 109, 3044-3079, incorporated herein by reference). In particular, Halichondrin B has been reported as a potent anticancer agent that was first isolated from the marine sponge Halichondria okadai (U.S. Pat. No. 5,436,238; Tetrahedron Lett. 1994, 35, 9435 and WO 1993/017690 A1, all incorporated herein by reference). It was further reported that analogs of Halichondrin B bearing only macrocyclic fragment of its molecule (C1-C30 fragment) and having a ketone function instead of ester at C1 position demonstrate anticancer activity similar to Halichondrin B (Bioorg. Med. Chem. Lett., 2000, 10, 1029 and Bioorg. Med. Chem. Lett., 2004, 14, 5551). It was established that such macrocyclic fragment is responsible for induction of mitotic blocks in cancer cells via disruption of tubulin polymerization process that triggers apoptosis of cancerous cells and stops their proliferation (Cancer Res., 2004, 64, 5760 and Mol. Canc. Ther., 2008, 7, 2003). Eribulin mesylate, a macrocyclic C1-keto analog of Halichondrin B, has been reported as having potent anticancer properties (WO 1999/065894 A1, incorporated herein by reference). Eribulin is marketed under the trade name Halaven, and it is also known as E7389, B1939 and ER-086526.

2,5-disubstituted (2S,5S)-3-methylene-tetrahydrofurans, such as the compound of formula 11a, can be an important building block for the synthesis of the halichondrin natural products and derivatives, as described in U.S. Pat. Nos. 6,214,865 and 5,436,238, and incorporated herein by reference.
wherein Piv is (CH3)3C—C(═O)—.
The synthesis of compounds, similar to the compound of formula 11a, has been described by Kishi (Pure Appl. Chem. 2003, 75, 1-17; J. Am. Chem. Soc. 2009, 131, 15642-15646; J. Am. Chem. Soc. 2009, 131, 15636-15641), Phillips (Angew. Chem., Int. Ed. 2009, 48, 2346) and Burke (Org. Lett. 2002, 4, 3411-3414, J. Org. Chem. 2003, 68, 1150-1153), all incorporated herein by reference. However, these methods can be undesirable for commercial manufacturing. For example, all these routes rely on asymmetric reactions that, despite their high degree of selectivity, can give rise to epimers, which are of particular concern in cases where the intended use of the molecule is in the manufacture of an active pharmaceutical ingredient. Furthermore, many of these asymmetric reactions employ chiral ligands that are not necessarily easily commercially available, and which can be a hindrance for large scale production.
A number of concerns were addressed in PCT/CA2012/050897 (filed Dec. 14, 2012, and incorporated herein by reference) that provided a route for synthesis of the compound of formula 11a. However, further improvements to improve scalability of the process, such as by improving yields of one or more synthetic steps, improving overall synthetic yield or avoiding or reducing the number of chromatographic purifications, by providing an alternate route to the synthesis of the compound of formula 11a can be desirable.
There is a need in the art for a process for preparation of 3-((2S,5S)-4-methylene-5-(3-oxopropyl)tetrahydrofuran-2-yl)propanol (11a), and its analogs (11), that can be used in the preparation of halichondrin natural products, its derivatives and analogs. In addition, there is a need in the art for a process for preparation of 3-((2S,5S)-4-methylene-5-(3-oxopropyl)tetrahydrofuran-2-yl)prop-1-yl pivaloate (11a), and its analogs (11), that can be prepared from commercially available starting material. Moreover, there is a need in the art for a process for the preparation of 3-((2S,5S)-4-methylene-5-(3-oxopropyl)tetrahydrofuran-2-yl)prop-1-yl pivaloate (11a), and its analogs (11), that can avoid the use of asymmetric reactions, including chiral ligands. In addition, there is a need in the art for a process for preparation of 3-((2S,5S)-4-methylene-5-(3-oxopropyl)tetrahydrofuran-2-yl)prop-1-yl pivaloate (11a), and its analogs (11), where the process is scalable and can lead to a product having high stereochemical purity.